With the rapid growth of LED television in recent years, correlation techniques are changed quickly, and market demand is rapidly increased. Particularly, the market share of edge type LED television is continuously increased because the edge type LED television has the advantages of beautiful appearance, low cost and high benefit. However, because the corresponding optical components of the edge type LED television are not supplied in time, there is a lack of supply of light guide plates (LGPs), dual brightness enhancement films (DBEFs) and PET optical diaphragms. In addition, with the continuous expansion of the production capacity of LEDs, the problem of lack of LED light sources is already solved. Thus, adding number of LEDs and reducing dependency on optical diaphragms, LGPs and DBEFs become the focus of development of each module factory.
A direct type LED TV module does not use an LGP. The LED distribution density of the direct type LED TV module is sparser than that of an edge type LED TV module, and low power LEDs do not require special design for heat dissipation. Adding number of LEDs to remove DBEF has a positive effect on cost. Meanwhile, direct type light sources are zonally controlled, and drive control and image compensation are performed in accordance with signal sources to increase image quality. However, the direct type LED TV module has the fatal disadvantages: a certain number of LEDs must be used to avoid producing LED mura, and light-boards must be used, resulting in high cost. Although uniformity is improved, adding the height of a back light cavity causes the luminance to be reduced (as shown in FIG. 1). Therefore, how to achieve balance among low cost, high efficiency and high quality when using minimum LEDs at appropriate height of the back light cavity by the LED lens design becomes a problem of the design of LED back light at present.